To make such a light emitting device suitable for both outdoor and indoor applications, full sealing of the substrate and the LEDs, i.e. the LED strip, is needed. Normally this is achieved by either inserting the LED strip in an extruded cover or by embedding the LED strip. The opposite ends of the light emitting device are normally sealed by endcaps and additional closing processes, such as gluing, welding, etc.
The substrate of such a LED-strip is normally flexible only in the thickness direction and has limited flexibility perpendicular to the thickness direction. The LED's are divided along the length of the substrate and have certain distances or a certain pitch with respect to each other. To keep the LED-strip as flexible as possible the cross section of the sleeve or embedding must be as thin as possible seen in the thickness direction of the substrate.
Currently two directions are commonly found to generate the desired lighting effect of such a LED-strip:
Generally, it is desired to achieve two different lighting effects with such a light emitting device, namely an indirect spotty lighting effect or indirect bright spotty lighting effect and a diffuse homogeneous lighting effect or direct diffuse homogeneous lighting effect.
US 2014/0126196 A1 discloses a light fixture which in one embodiment comprises a transparent or diffusing body with a channel for wiring and a further channel for receiving a reflector with LEDs mounted thereon, and a cover with a lens forming a light exit surface. The body and the core are connected or connectable by means of mutually engaging attachment portions.
In the prior art solutions, to obtain an indirect, spotty lighting effect, a thin sleeve being transparent or translucent is used to seal the LED strip. Mounting is normally done in tucked away areas and the observer or user will normally only see the indirect lighting effect of the LED-strip reflecting on e.g. a wall or, for outdoor applications, a fence, plants, or the like. The reason for hiding the LED strip is that the bright spotty lighting of the LEDs are not friendly for the eye to look at since as a requirement in indirect lighting applications the LEDs have to be very bright. This solution can be found in cheap consumer solutions which not always are fully suitable for outdoor use.
For quite a few applications in the outdoor or indoor environment, the indirect lighting effect does not always provide a nice lighting solution as i.e. limited white walls are available. For such applications a direct view on the LED-strip would be desired. To this end a direct, diffuse, homogeneous lighting effect is desirable.
In the prior art solutions, such a direct, diffuse, homogeneous lighting effect is normally obtained by making a less bright, diffuse and homogeneous lighting line. Technically this has been achieved by means of several different solutions, such as:
decreasing the LED-pitch so LEDs are arranged closer to each other,
increasing the optical path from LED to exit surface of the sleeve, and
adding diffusing materials to the sleeve which enable mixing of the light before emission.
The most commonly found prior art solution to create a homogeneous lighting LED strip is to place the LED strip vertical, and bending the light 90 degrees with a light guiding material. For this solution a white reflective surround is also needed. The exit surface of the LED-strip is then on top and has a diffuse character. The light from the LEDs is then mixed over a long distance by the light guide and finally mixed in the diffuse exit window. This solution is quite complex and expensive. It can be found in professional LED-strip solutions, but is quite bulky and inflexible.
Another solution is to mount Al-profiles with diffuse plastic covers. Not in all cases are these profiles constructed for outdoor and are not watertight and not always big enough to allow the cross sectional size needed for an LED strip rated for outdoor applications.
Also, the optical construction around a diffuse outdoor/indoor LED strip comprises a high number of components and is thus quite complex and expensive.
Furthermore, solutions employing diffusing elements normally exhibit a very low optical efficiency, and may range from well executed solutions with an optical efficiency of ˜50-60% to very bad executions with an optical efficiency as low as <30%. The spotty solutions are normally better in efficiency and only have very low losses in the transparent/translucent materials.
Also, consumers might not be aware that there is quite some difference between a spotty and a diffuse lighting effect. Selecting the right solution may be difficult and selection of the wrong solution may lead to unsatisfied consumers.